It can happen at the beginning or ending of an egg cycle for an older hen as with a point of lay pullets.
When they first started laying we kept looking for the tiny "starter" eggs, but never found any. These three are just over a year old and have been laying for awhile now so my son was surprised to find this. LOL My husband jokes that the one must finally be deciding to lay, but I think she has been laying already. She is just smaller than the others weight wise.